We plan to attempt to demonstrate biosynthesis of 24- hydroxycholesterol in myelin and other defined subcellular fractions of rat brain and to demonstrate metabolism of 24-hydroxycholesterol in these fractions using 24-H3- or 4-C14-24-hydroxycholesterol. Both intracerebral injections in intact animals and incubations using brain homogenates and defined subcellular fractions will be examined, and sterol metabolites from both experiments will be isolated and identified. These and other suspected metabolites will be sought for in human brain (from autopsy). Studies will be made with both adult rat brain and with developing rat brain. Chemical synthesis of the required labeled 24-hydroxycholesterol will be made. We will analyze defined cell types (glial versus neuronal, etc.) of human and rat brain for their 24-hydroxycholesterol and 24-hydroxycholesterol metabolites content. We will attempt to examine some physico-chemical effects of 24-hydroxycholesterol on properties of model membrane systems.